Add the light only if you can manage the heat.
Your nug shots look pretty good, but to the trained eye they don't look dense. That's because your temps are high. They're getting good light, so growth is good, but they have trouble establishing density in higher temps. That third shot especially looks on the airy side. You won't be thrilled with the harvest if you just keep increasing light without managing heat.
edit:
But it could just be the way the strain is developing... Since your leaves don't look heat stressed. didn't realize you were only three weeks in. Plenty of time to dense up. Sorry for jumping the gun.